This application is submitted in response to NIAAA's program announcement, Behavioral & Integrative Treatment Development Program, PA-10-013 and is consistent with NIH's recent interest in developing adaptive mobile interventions. The proposed development study entitled, Tailored Mobile Text Messaging to Reduce Problem Drinking is designed to develop and test a tailored adaptive text messaging/short message service (SMS) intervention for individuals interested in stopping or reducing their alcool consumption. Excessive alcohol consumption is a serious personal and public health issue and economic problem to society. Despite the significant consequences of problem drinking (PD), most persons with alcohol problems never seek formal treatment. While the emergence of internet based interventions (IBIs) has expanded access and brief intervention opportunities to problem drinkers, traditional IBIs suffer from high attrition, limited ability to proactively meet individuals where PD occurs and adapt to real-time needs. Recent evidence from smoking cessation studies highlight that SMS interventions may provide the needed reinforcement to help individuals enhance self-regulation and reduce problem alcohol use when they need it most in their natural environment. Moreover, because PD typically has regular episodic patterns, tailored interactive designs may be particularly effective. This study is designed to develop and test an interactive adaptive mobile messaging intervention for PD, which includes messages tailored to baseline assessment results (including drinking times) that are adaptive to ongoing drinking patterns and goal achievement via interactive ecological momentary assessment (EMA). Other features include participant initiated help messaging and support network alerts. We will conduct beta research with 40 problem drinkers to assess messaging preferences and acceptability, and then conduct a pilot test with 10 PDs. In Stage 1b, we aim to test this intervention and understand the mechanisms of action of different text messaging interventions with 200 problem drinkers over a 12-week period. We propose to compare four types of messaging: 1) Tailored content and timed messaging adaptive to the participants current state (Stage 1a intervention)~ 2) Tailored content messaging (not adaptive or timed) sent at 3 pm every day~ 3) Untailored consequence based messages sent at 3 pm every day~ and 4) Brief feedback and EMA only. Assessments will be completed at baseline, through weekly EMA via SMS and at week 12 via a web-based follow-up assessment. Primary outcomes include drinks per drinking day, days of heavy drinking, and average drinks per week as measured through weekly EMA. Additional outcomes will include drinking related consequences, goal commitment and intervention satisfaction. Outcomes will be used to modify the intervention and to prepare for a larger Stage 1c RCT.